Currently, CIS based thin film solar cells are widely put into practical use. It is known that, when the CIS based thin film solar cells are manufactured, a thin film solar cell having a high conversion efficiency can be obtained by growing a cadmium sulfide (CdS) layer as a high-resistance buffer layer on an light absorbing layer made of a CuInSe2-based thin film.
Patent Document 1 discloses a chemical bath deposition (CBD) method for chemically depositing a cadmium sulfide (CdS) thin film from a solution by immersing a CuInSe2 thin film light absorbing layer in a solution so that a thin film light absorbing layer and a high-quality heterojunction can be formed, and shunt resistance can increase.
In addition, Patent Document 2 discloses a method of manufacturing a thin film solar cell having a high conversion efficiency, as in the case where the cadmium sulfide (CdS) layer is used as a buffer layer, by using a zinc mixed-crystal compound, i.e., Zn(O,S,OH)x composed of oxygen, sulfur, and a hydroxyl group chemically grown from a solution on a p-type light absorbing layer as the high-resistance buffer layer.
Furthermore, Patent Document 3 discloses a technique of manufacturing a thin film by successively depositing a buffer layer and a window layer on a glass substrate in that order using a metal organic chemical vapor deposition (MOCVD) method.    Patent Document 1: U.S. Pat. No. 4,611,091    Patent Document 2: Japanese Patent No. 3249342    Patent Document 3: JP-A-2006-332440